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/* ****************************************************************************
*
* Copyright (c) Microsoft Corporation.
*
* This source code is subject to terms and conditions of the Apache License, Version 2.0. A
* copy of the license can be found in the License.html file at the root of this distribution. If
* you cannot locate the Apache License, Version 2.0, please send an email to
* dlr@microsoft.com. By using this source code in any fashion, you are agreeing to be bound
* by the terms of the Apache License, Version 2.0.
*
* You must not remove this notice, or any other, from this software.
*
*
* ***************************************************************************/
using System;
using System.Diagnostics;
#if CLR2
namespace Microsoft.Scripting.Ast {
#else
namespace System.Linq.Expressions {
#endif
/// <summary>
/// Represents the default value of a type or an empty expression.
/// </summary>
#if !SILVERLIGHT
[DebuggerTypeProxy(typeof(Expression.DefaultExpressionProxy))]
#endif
public sealed class DefaultExpression : Expression {
private readonly Type _type;
internal DefaultExpression(Type type) {
_type = type;
}
/// <summary>
/// Gets the static type of the expression that this <see cref="Expression" /> represents.
/// </summary>
/// <returns>The <see cref="Type"/> that represents the static type of the expression.</returns>
public sealed override Type Type {
get { return _type; }
}
/// <summary>
/// Returns the node type of this Expression. Extension nodes should return
/// ExpressionType.Extension when overriding this method.
/// </summary>
/// <returns>The <see cref="ExpressionType"/> of the expression.</returns>
public sealed override ExpressionType NodeType {
get { return ExpressionType.Default; }
}
/// <summary>
/// Dispatches to the specific visit method for this node type.
/// </summary>
protected internal override Expression Accept(ExpressionVisitor visitor) {
return visitor.VisitDefault(this);
}
}
public partial class Expression {
/// <summary>
/// Creates an empty expression that has <see cref="System.Void"/> type.
/// </summary>
/// <returns>
/// A <see cref="DefaultExpression"/> that has the <see cref="P:Expression.NodeType"/> property equal to
/// <see cref="F:ExpressionType.Default"/> and the <see cref="P:Expression.Type"/> property set to <see cref="System.Void"/>.
/// </returns>
public static DefaultExpression Empty() {
return new DefaultExpression(typeof(void));
}
/// <summary>
/// Creates a <see cref="DefaultExpression"/> that has the <see cref="P:Expression.Type"/> property set to the specified type.
/// </summary>
/// <param name="type">A <see cref="System.Type"/> to set the <see cref="P:Expression.Type"/> property equal to.</param>
/// <returns>
/// A <see cref="DefaultExpression"/> that has the <see cref="P:Expression.NodeType"/> property equal to
/// <see cref="F:ExpressionType.Default"/> and the <see cref="P:Expression.Type"/> property set to the specified type.
/// </returns>
public static DefaultExpression Default(Type type) {
if (type == typeof(void)) {
return Empty();
}
return new DefaultExpression(type);
}
}
}
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